Room Temperature Growth Research Articles

Room temperature deposited highly conductive HfNx films for high-performance HfN/Si junction diodes

Transition metal nitrides are valuable materials for many technological applications due to their favorable physical characteristics, including conductivity, high temperature stability, and hardness. Among them, hafnium nitride (HfN) thin films of high attributes are crucial for semiconductor applications. However, achieving performance efficiency of HfN films with desired electrical performance via conventional deposition methods is a challenging task. Herein, we have achieved room temperature growth of highly oriented cubic HfN thin film grown on Si substrate by process optimization of radio frequency (RF) magnetron sputtering. HfN thin films were structurally, morphologically, and electrically characterized. The metallic behavior of HfN films was confirmed through current-voltage measurements; it showcased excellent electrical conductivity, signifying low resistivity (≈ 0.55 kΩ sq-1), revealing promising evidence for its potential practical application. Moreover, the first-principles calculations were also conducted to gain further insights into the electrical performance of the HfN films. These findings lay a solid foundation for further exploration and development of HfN-based junction diodes, as the observed characteristics offer significant potential for enhancing device performance in various electronic domains.

Room-Temperature Growth of Square-Millimeter Single-Crystalline Two-Dimensional Metal Halides on Silicon.

Silicon is the cornerstone of electronics and photonics. In this context, almost all integrated devices derived from two-dimensional (2D) materials stay rooted in silicon technology. However, as the growth substrate, silicon has long been thought to be a hindrance for growing 2D materials through bottom-up methods that require high growth temperatures, and thus, indirect routes are usually considered instead. Although promising growth of large-area 2D materials on silicon has been demonstrated, the direct growth of single-crystalline materials using low-thermal-budget synthesis methods remains challenging. Here, we report the room-temperature growth of millimeter-scale single-crystal 2D metal halides on silicon substrates with a hydroxyl-terminated surface. Theoretical calculations reveal that the activation energy for surface diffusion can be reduced by an order of magnitude by terminating the surface with hydroxyl groups, from which on-silicon growth is greatly facilitated at room temperature and enables a 4-order-of-magnitude increase in area. The high quality and uniformity of the resulting single crystals are further evidenced. The optoelectronic devices employing the as-grown materials show an ultralow dark current of 10-13 A and a high detectivity of 1013 Jones, thereby corroborating a weak-light detection ability. These results would point to a rich space of surface modulation that can be used to surmount current limitations and demonstrate a promising strategy for growing 2D materials directly on silicon at room temperature to produce large single crystals.

Tin oxide thin films on Ag(111): Thickness and temperature dependent study of surface structure and electronic properties

Growth and structure of tin oxide films on Ag(111) from submonolayer to 10 monolayer equivalent thickness have been studied using low energy electron diffraction (LEED), x-ray photoemission spectroscopy (XPS) and angle-resolved photoemission spectroscopy techniques for room temperature (RT) and high temperature (HT) (573 K). For RT growth, most of the tin is oxidised to form tin oxide (SnOx) as confirmed by XPS where no metallic component is noticed. However, the grown films are not epitaxial or ordered which can be confirmed by no spots in LEED for higher coverage. Metallic Sn along with two oxidation states of Sn are noticed for HT growth, with the surface mainly composed of SnO2. LEED pattern shows the presence of c(2 × 2) and (3 × 1) along with two different hexagonal multidomain type patterns. The electronic structure for lower coverage resembled the Sn/Ag(111) alloy structures for lower coverage. For higher coverages appearance of three bands below 2 eV binding energy was noticed.

Room temperature growth of CsPbBr3 single crystal for asymmetric MSM structure photodetector

UV–visible broadband light harvesting ability is critical for photodetectors, and all inorganic perovskite CsPbBr3 is regarded as a promising candidate as the response active material. Herein, a saturated-solution crystallization method is employed to synthesize CsPbBr3 single crystal. Temperature-dependent photoluminescence spectra with one-photon and two-photon excitation are systematically investigated, determining a large exciton binding energy of 39.8 meV. This allows the stable excitonic emission of CsPbBr3 single crystal at room temperature. Subsequently, an asymmetric structure CsPbBr3 photodetector is fabricated by using InGa alloy as the Ohmic electrode and Au as the Schottky electrode. At -8 V, the device exhibits a prominent response to the irradiation from UV to green band with a maximum responsivity of 2.56 A/W, an external quantum efficiency of 580 %, and a detectivity of 1.24 × 1013 Hz1/2 W−1. In addition, the CsPbBr3 photodetector also presents rapid response speeds at both reverse and forward bias voltages and self-powered characteristics owing to the Schottky depletion layer underneath the Au electrode. The demonstration of asymmetric metal-semiconductor-metal (MSM) structure photodetector presents a promising pathway toward next-generation CsPbBr3 optoelectronic devices.

Extracting mechanical and microstructural properties of Cu–Zr thin film alloys by MEMS, AFM and ellipsometer

The quantification of the atomic concentration ratios of thin-film metallic alloys having low atomic ordering is challenging, particularly if they are grown on similar metals and possess different surface chemistries. Micromechanical and optical methods have been used to correlate the elemental ratios with the mechanical and optical properties of the films. The room-temperature growth of Cu–Zn thin-film alloys with varying elemental ratios on cosputtered Si substrates was performed to obtain an amorphous film structure. X-ray diffraction patterns confirmed that the grown films exhibited a very short range ordering, suggesting an amorphous structure. The mechanical properties of the films evaluated using microelectromechanical system (MEMS) indicated that the alloy films with moderate Zr concentrations had lower surface stress compared to those with low and high Zr concentrations. Furthermore, spectroscopic ellipsometry was employed to qualitatively assess the relaxation times of free carriers. The results demonstrated a strong correlation between the relaxation times and surface roughness measurements, showing that the microstructure and resistivity characteristics of the alloys align with the Nordheim semiempirical model. The extinction coefficient of the binary alloy film linearly depends on the metallic bulk concentration ratio in a specific metallic ratio range, paving the way for realizing qualitative elemental percentage assessment in the field of metrology.

Room temperature growth of NiS hierarchical nanoflowers on the flexible electrode surface as a cathode for lithium-ion batteries

A facile additive-free approach of cathode fabrication using a chemical bath deposition route is proposed to grow nickel sulfide nano-architectures on Ni foam at ambient conditions as a flexible electrode for lithium-ion batteries. The hierarchical nanostructure on the electrode surface provided high specific capacities of 437 and 360 mAh/g at current rates of 0.1 and 1.0C after 50cycles respectively, accompanied by Coulombic efficiency of about 100% after only 5 cycles. The designed electrodes offered a faster ion and electron transfer, a larger surface area, and a high degree of structural integrity.

Room-temperature growth of perovskite single crystals via antisolvent-assisted confinement for high-performance electroluminescent devices

Organic-inorganic halide perovskite single crystals (OIHP-SCs) are promising light-emitting materials for bright electroluminescence (EL) devices due to their superior optoelectronic properties and excellent stability. However, the conventional high-temperature growth methods will inevitably disturb the ordered growth and introduce massive defects in OIHP-SCs, leading to the degradation of device performance. The preparation of thin OIHP-SCs with low trap-state densities for high-performance EL devices remains a formidable challenge. Here, we develop an efficient antisolvent-assisted confined growth (AACG) method for the room-temperature growth of formamidinium lead bromide (FAPbBr3) perovskite SCs. An antisolvent vapour environment is intentionally introduced in the spatially confined growth process to lower the free energy barrier for nucleation, enabling the growth of high-quality FAPbBr3 SCs at room temperature. Consequently, FAPbBr3 SCs with ultralow trap-state density of 2.15 × 109 cm−3 and amplified spontaneous emission (ASE) threshold of 7.1 µJ cm−2 could be achieved, representing the best results ever reported for FAPbBr3 SCs. By leveraging the high crystal quality of FAPbBr3 SCs, SC-based perovskite light-emitting diodes (PeLEDs) with a high luminance of over 26,000 cd m−2 and a peak current efficiency (CE) of 13.02 cd A−1 are demonstrated. Our work opens up new opportunities for the development of high-performance EL devices based on OIHP-SCs.

Low-Temperature Plasma Oxidation of Aluminum by Ar-O2 Mixtures in a Dielectric-Barrier Discharge Reactor

Room-temperature growth of oxide layers on aluminum in highly diluted mixtures of oxygen with argon (O2 molar fractions 20 ppm ≤ x_{O_2} ≤ 500 ppm, partial pressures 2 Pa ≤ p_{O_2} ≤ 50 Pa) flowing through a dielectric-barrier discharge (DBD) reactor is studied, including oxidation in the pre- and post-discharge regions (PrD, PoD) adjacent to the main DBD. Three different mechanisms of plasma-enhanced oxidation were found to prevail, depending on the location of the sample: (1) In the close PrD region, up to 1 cm upstream from the discharge, accelerated growth of Al2O3 is due to the irradiation of the sample surface by highly energetic (9.8 eV) argon excimer radiation in the presence of O2. (2) In the remote PoD, a few cm downstream from the DBD, oxidation can largely be attributed to oxygen atoms, with number densities typically between 1 and 5 × 1014 cm−3. Here, analysis in terms of Cabrera–Mott (CM) theory results in CM potentials between − 1.5 and − 2.1 V. (3) In the DBD itself both O atoms and VUV photons generally play an important role but, under special conditions, an additional oxidation mode can be identified, characterized by a much larger limiting thickness: While, in general, oxide growth by O atoms and/or VUV photons virtually stops at thicknesses X between 5 and 6 nm, much thicker oxide films can be achieved in the downstream region of the main DBD, with thicknesses growing with the length of the DBD zone. Tentatively, we attribute this observation to negative oxygen ions Om− (1 ≤ m ≤ 3) accumulating in the gas while passing the reactor. Any direct electrical effects of the discharge process on the oxidation can probably be neglected.

Room-Temperature Growth of Morphoplastic Scandium Nanowires through Coordination-Induced Self-Assembly for White-Light-Driven Photocatalytic Degradation of Rhodamine

Photoactive nanowires play an important role on the photoelectric-related applications; however, the in situ large-scale growth of photoactive nanowires on the arbitrary substrate still faces a great challenge. Herein, for the first time, we develop a facile coordination-induced self-assembly strategy for preparing the nanowires with high photoactivity through keeping a high concentration of Sc(NO3)3 and tartaric acid (TA) aqueous solution at room temperature. Surprisingly, the nanowires can grow directionally along the direction of water flow on any substrate due to the growth mechanism driven by water molecules, showing that the proposed nanowires are morphoplastic depending on the direction of liquid flow. The formation of nanowires has been proved to be attributed to the synergistic effect of water molecule-involved hydrogen bonding between hydroxyl groups of TA ligands as well as the multi-coordination of Sc3+ ions. Meanwhile, the prepared nanowires are highly photoactive, showing a strong photooxidation ability toward rhodamine 6G dyes, with a degradation efficiency of about 95.8% within 40 min. This finding introduces a coordination growth mechanism of nanowires, which not only provides a great possibility for large-scale and low-cost synthesis of photoactive nanowires with morphoplastic features but also shows a good application prospect in water cleaning by the photocatalysis technique.

Local hybridized states of adsorbed atomic Sn on WS2 substrate

We study the growth of Sn and the local electronic properties of Sn grown WS2 surfaces by in-situ scanning tunneling microscopy (STM), scanning tunneling spectroscopy, and first principles density functional theory calculations. Our investigations suggest substitutional doping of Sn at the S sites, with Sn atoms occupying a slightly elevated position of 80 pm on the WS2 surface. These results agree well with our STM observations on room temperature growth of atomic Sn, indicating commensurate or nearly commensurate adsorption at the top S sites with a buckling height of 40 ± 10 pm. Pristine WS2 without any S vacancies on the surface exhibits a bandgap of 1.39 eV, while ingap local density of states comprised of W d and S p orbitals are detected when S vacancies are considered. Upon adsorption of Sn atoms, we find the signature of modulated hybridized ingap electronic states of Sn p and W d orbitals with a spin orbit coupling interaction up to 38 meV at the K point of the Brillouin zone. These results throw important light on the future fabrication of Janus like SnWS vertical heterojunctions with atomic level doping accuracy, which will have enormous device applications.

Temperature-specific adaptations and genetic requirements in a biofilm formed by Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a gram-negative opportunistic pathogen often associated with nosocomial infections that are made more severe by this bacterium's ability to form robust biofilms. A biofilm is a microbial community encompassing cells embedded within an extracellular polymeric substrate (EPS) matrix that is typically secreted by the encased microbial cells. Biofilm formation is influenced by several environmental cues, and temperature fluctuations are likely to be an important stimulus in the lifecycle of P. aeruginosa as it transitions between life in aquatic or soil environments to sites of infection in the human host. Previous work has demonstrated that human body temperature can induce a shift in the biofilm EPS relative to room temperature growth, resulting in an incorporation of a filamentous phage coat protein into the biofilm EPS. In this study, we sought to identify adaptations enabling biofilm formation at room temperature or temperatures mimicking the natural environment of P. aeruginosa (23°C and 30°C) relative to temperatures mimicking life in the human host (37°C and 40°C). We identified higher biofilm: biomass ratios at lower temperatures on certain substrates, which correlated with a higher relative abundance of apparent polysaccharide EPS content. However, the known genes for EPS polysaccharide production in P. aeruginosa PA14 did not appear to be specifically important for temperature-dependent biofilm adaptation, with the pelB gene appearing to be generally important and the algD gene being generally expendable in all conditions tested. Instead, we were able to identify two previously uncharacterized hypothetical proteins (PA14_50070 and PA14_67550) specifically required for biofilm formation at 23°C and/or 30°C relative to temperatures associated with the human host. These unstudied contributors to biofilm integrity may have been previously overlooked since most P. aeruginosa biofilm studies tend to use 37°C growth temperatures. Overall, our study demonstrates that temperature shifts can have dramatic impacts on biofilm structure and highlights the importance of studying environment-specific adaptations in biofilm physiology.

Unravelling the room temperature growth of two-dimensional h-BN nanosheets for multifunctional applications.

The room temperature growth of two-dimensional van der Waals (2D-vdW) materials is indispensable for state-of-the-art nanotechnology. Low temperature growth supersedes the requirement of elevated growth temperatures accompanied with high thermal budgets. Moreover, for electronic applications, low or room temperature growth reduces the possibility of intrinsic film-substrate interfacial thermal diffusion related deterioration of the functional properties and the consequent deterioration of the device performance. Here, we demonstrated the growth of ultrawide-bandgap boron nitride (BN) at room temperature by using the pulsed laser deposition (PLD) process, which exhibited various functional properties for potential applications. Comprehensive chemical, spectroscopic and microscopic characterizations confirmed the growth of ordered nanosheet-like hexagonal BN (h-BN). Functionally, the nanosheets show hydrophobicity, high lubricity (low coefficient of friction), and a low refractive index within the visible to near-infrared wavelength range, and room temperature single-photon quantum emission. Our work unveils an important step that brings a plethora of potential applications for these room temperature grown h-BN nanosheets as the synthesis can be feasible on any given substrate, thus creating a scenario for "h-BN on demand" under a frugal thermal budget.

In Situ Growth and UV Photocatalytic Effect of ZnO Nanostructures on a Zn Plate Immersed in Methylene Blue

Nanostructures of zinc oxide (ZnO) are considered promising photocatalysts for the degradation of organic pollutants in water. This work discusses an in situ growth and UV photocatalytic effect of ZnO nanostructures on a Zn plate immersed in methylene blue (MB) at room temperature. First, the Zn surfaces were pretreated via sandblasting to introduce a micro-scale roughness. Then, the Zn plates were immersed in MB and exposed to UV light, to observe ZnO nanostructure growth and photocatalytic degradation of MB. Scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-Vis diffuse reflectance spectroscopy were used to characterize the Zn surfaces. We observed the growth of stoichiometric and crystalline ZnO with a nano-leaf morphology and an estimated bandgap of 3.08 eV. The photocatalytic degradation of MB was also observed in the presence of the ZnO nanostructures and UV light. The average percentage degradation was 76% in 4 h, and the degradation rate constant was 0.3535 h−1. The experimental results suggest that room temperature growth of ZnO nanostructures (on Zn surfaces) in organic dye solutions is possible. Furthermore, the nanostructured surface can be used simultaneously for the photocatalytic degradation of the organic dye.

Preparation and gas separation performance of seeding-free aqueous synthesis ZIF-8 membrane by homologous-like ligands method

Due to the poor heterogeneous nucleation properties of MOFs crystal on ceramic substrates resulting from the absence of interaction of MOFs with support substrate surface, it is usually difficult to prepare well-intergrown MOF membranes on substrate by simple in situ growth. In this work, a novel synthesis strategy was used to prepare defect-free ZIF-8 membranes on α-Al2O3 supports by depositing gold particles modified with 2-mercaptoimidazole which creates pseudo-surfaces to bridge the metal centers with support. The end groups of the 2-mercaptoimidazole guides the heterogeneous nuclei to the support surface as homologous-like ligands. Furthermore, investigation of the metal sources revealed that the ZIF-8 membranes prepared with Zn(OAc)2 as the zinc source possessed more continuous and well-intergrown ZIF-8 membranes with a thickness of about 1 μm compared to other zinc sources. The results of gas separation performance show that the optimized ZIF-8 membranes possess high hydrogen permeance and thermal stability. The gas separation selectivity for binary H2/CH4 mixture reached 20.8 at 150 °C and 1 bar, with a high H2 permeance of about 6.15 × 10−7 mol m−2 s−1Pa−1, which is promising for hydrogen separation and purification. Moreover, free-organic solvents and room temperature growth by our strategy dramatically reduces the difficulty of preparation and environmental destruction, thus offering a new avenue to prepare MOFs membrane with good separation performance.

Regulating Co-MOF array films to construct Co3O4 in-situ sensors for ultrasensitive and highly selective triethylamine detection

Sensing films with controllable thickness and open-space array structures are desperately desired for practical application. In addition, in-situ gas sensors based on MOFs -derived MOSs films have been rarely reported. Herein, a room-temperature growth approach was proposed to fast prepare controlled Co-MOF arrays films on the substrates with interdigital electrodes. The as-prepared precursor films were further annealed to obtain Co3O4 in-situ sensors. This work systematically investigated the morphologies, structures, contact characteristics, and oxygen species of sensing films. It was found that they have apparent effects on the triethylamine sensing behaviors, thus obtaining the optimized gas sensor. The sensor exhibited excellent sensing performance, including fast response (from 82 s to 9 s), high sensitivity (Rg/Ra=230), and improved selectivity, compared to the Co3O4 sensor derived from non-MOF precursor films. The excellent triethylamine sensing performance benefited from the abundant oxygen vacancies and conducting channels. This work provides a simply-effective strategy for large-scale fabrication of in-situ gas sensors.

Near Room-Temperature Synthesis of Vertical Graphene Nanowalls on Dielectrics.

Vertical graphene nanowalls (VGNs) with excellent heat-transfer properties are promising to be applied in the thermal management of electronic devices. However, high growth temperature makes VGNs unable to be directly prepared on semiconductors and polymers, which limits the practical application of VGNs. In this work, the near room-temperature growth of VGNs was realized by utilizing the hot filament chemical vapor deposition method. Catalytic tantalum (Ta) filaments promote the decomposition of acetylene at ∼1600 °C. Density functional theory calculations proved that C2H* was the main active carbon cluster during VGN growth. The restricted diffusion of C2H* clusters induced the vertical growth of graphene nanoflakes on various substrates below 150 °C. The direct growth of VGNs successfully realized the excellent interfacial contact, and the thermal contact resistance could reach 3.39 × 10-9 m2·K·W-1. The temperature of electronic chips had a 6.7 °C reduction by utilizing directly prepared VGNs instead of thermal conductive tape as thermal-interface materials, indicating the great potential of VGNs to be directly prepared on electronic devices for thermal management.

Room-temperature growth optimization and PL characteristic of polytype h/α-MoO3 thin films by chemical precipitation method

In this study, MoO3 thin films were coated using a simple chemical precipitation technique at room temperature, without using an autoclave or other complex equipment. Films were deposited on precoated MoO3 seed layers prepared by spray pyrolysis on glass substrates. The effects of the seed layer growth conditions and pH value of the precipitation method’s solution on the characteristics of MoO3 films were investigated. The Raman and X-ray diffraction techniques showed that MoO3 films have grown in mixed hexagonal (h) and orthorhombic (α) crystal structures and the scanning electron microscope verified that the samples’ surface was covered of both hexagonal micro rods and lamellar micro belts. The XRD patterns indicated that the crystallinity was significantly improved using a seed layer sprayed under lower carrier gas pressure, and lower pH value of the precipitation method’s solution. The UV–Visible spectra showed that using seed layers prepared at higher carrier gas pressure decreases the bandgap of the films prepared by precipitation, due to the incorporation of more oxygen vacancies. The photoluminescence studies showed that the film deposited at a higher solution’s pH value has higher PL intensity, which indicates that this sample is a suitable candidate for optoelectronic applications.

Growth and morphology of thin epitaxial Pd films on Au(001) film grown on Fe-buffered MgO(001) substrate

We have investigated the growth of thin Pd films on a Au(001) surface, which was a Au(001) film grown on a Fe-buffered MgO(001) substrate, at 290 K up to 4 monolayer (ML) thickness and the effect of post-annealing (PA) at 470 K. The surface morphology and structure are determined using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). The LEED patterns of the as-grown and PA films indicate that the Pd(001) films grow epitaxially on the Au(001) surface with noticeable in-pain lattice expansion of 4.5% relative to the bulk Pd, indicating a tensely strained tetragonal deformation. The Pd film does not grow in the layer-by-layer growth mode at 290 K. Instead, numerous Pd islands grow anisotropically along the 〈110〉 direction. The surface morphology of the films improves significantly after the PA at 470 K due to the coalescence of the elongated Pd islands. Consequently, the room temperature growth of the Pd layers followed by PA at 470 K enables us to fabricate the high-quality epitaxial Pd(001) film, which has large and atomically flat terraces without Au segregation. Additional Pd growth up to 8 ML thickness onto such 4 ML PA films kept at 470 K is also studied by STM. This specific three-step method facilitates the quasi-layer-by-layer growth and opens a chance for practical use in the future.

Room-temperature growth of fluorapatite/CaCO3 heterogeneous structured composites inspired by human tooth.

Organisms can synthesize heterogeneous structures with excellent mechanical properties through mineralization, the most typical of which are teeth. The tooth is an extraordinarily resilient bi-layered material that is composed of external enamel perpendicular to the tooth surface and internal dentin parallel to the tooth surface. The synthesis of enamel-like heterostructures with good mechanical properties remains an elusive challenge. In this study, we applied a biomimetic mineralization method to grow fluorapatite/CaCO3 (FAP/CaCO3) heterogeneous structured thin films that mimic their biogenic counterparts found in teeth through a three-step pathway: coating a polymer substrate, growing a layered calcite film, and mineralization of a fluorapatite columnar array on the calcite layer. The synthetic heterostructure composites combine well and exhibit good mechanical properties comparable to their biogenic counterparts. The FAP/CaCO3 heterogeneous structured composite exhibits excellent mechanical properties, with a hardness and Young's modulus of 1.99 ± 0.02 GPa and 47.5 ± 0.6 GPa, respectively. This study provides a reasonable new idea for unique heterogeneous structured materials designed at room temperature.

Room Temperature Growth of Silica Nanowires on Top of Ultrathin Si Nanowires Synthesized with Sn‐Cu Bimetallic Seeds

Si nanowires (NWs) are grown by the vapor–liquid–solid method using Cu–Sn bimetallic catalysts in a plasma‐enhanced chemical vapor deposition (PECVD) reactor. The microstructure of the NWs is analyzed by transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. An amorphous SiO2 region, much larger than the native oxide, is present on top of each crystalline SiNW: in SiNWs with diameter below 10 nm, it takes the form of a silica NW of up to 50 nm in length. The new NW separates the initial catalyst particle into one that stays in contact with the SiNW and one or more that lies at the top of the new NW. The former is made of Cu and Cu3Si and contains no Sn, whereas the latter keeps amounts of both elements. The observed microstructure appears to be the result of a mechanism of Si oxidation catalyzed by Cu3Si. The deposit after SiNW growth, in the PECVD reactor, of a protecting 2 nm thick layer of hydrogenated amorphous Si, completely suppresses this mechanism. Reference for future applications based on Cu–Sn‐catalyzed quantum‐sized SiNWs is provided.